The aim of the present study is to determine the clinical, intellectual and behavioral significance of variation in the human karotype as studied by a combination of Q, G, and C banding and previously determined clinical, intellectual etc. factors. Since antenatal diagnosis determination of the chromosome complement is being employed with increasing frequency a study of the present type of essential in order to provide information about the phenotypes of chromosomal variants from a relatively unbiased population. Such data is essential for adequate counseling of families where antenatal diagnosis is being carried out. The proposed research will permit completion of an going project in about 7,500 children by these new technics and a final analysis of the data based on information acquired about the children at ages 7 and 8. Specific objectives include delineation of racial differences, differences in IQ, birth weight, congenital anomalies in respect to each of the more than 6 chromosomal polymorphisms now being detected in each child. It is anticipated that a total of about 50 children will be ascertained with major chromosomal abnormalities; information about these children will assist materially in determining the variation and extent of phenotypic abnormalities in many of the major chromosomal abnormalities.